This invention relates generally to cellular communications and applications, and more particularly to a method and system of delivering Time Of Arrival (TOA) positioning data to at least one externally operated and maintained requesting agent.
The increased demand for wireless (or cellular) communications has resulted in advanced communications systems capable of providing a high quality of service to more users. The systems that have emerged include analog systems as Advanced Mobile Phone System (AMPS), and digital systems such as the Global System for Mobile Communications (GSM) and Digital AMPS (D-AMPS). To implement these systems, cellular based communication devices operate in interference-limited environments, that rely on frequency reuse plans to maximize capacity and quality. Protocols such as the Frequency Division Multiple Access (FDMA) in analog systems, and the Time Division Multiple Access (TDMA) in digital systems are used for this purpose.
In traditional wire line telephone systems, such as the Public Switched Telephone Network (PSTN), location of the telephone user was facilitated by associating the user with a service location. In wireless environments, determining the location of the user is much more complex since roaming within the network is permitted. Typically, triangulation systems are employed to permit positioning as a function of signal strength from at least three receiving entities in the network.
As the use of Wireless communication systems increases, so does the importance of determining the location or xe2x80x9cpositioningxe2x80x9d of users within the network. Positioning algorithms and systems are being developed and used to calculate and render positioning coordinates of a user. At the same time, positioning has become mandated by government agencies (i.e., FCC) as a standard to be implemented as early as the year 2001. In order to prepare for such implementation, the industry as a whole has been working on this effort as evidenced in Reference RTS/SMG-030378QR1 (Digital cellular communication system (Phase 2+); Location Services (LCS); GSM).
The Time of Arrival (TOA) positioning mechanism is based on collecting time of arrival (TOA) measurements computed from access bursts generated by the mobile set. Access bursts are generated during intracell handover and are received and measured by both serving and neighboring base stations. Utilizing access bursts to position the mobile requires additional hardware at the listening BTSs to accurately measure the TOA of the bursts.
A problem with prior art, positioning systems is that the current TOA positioning architecture is based on communication of Location Management Unit (LMU) and the Serving Mobile Location Center (SMLC) over an air interface using Direct Transfer Access Protocol (DTAP) messages. In this regard, the SMLC is used to describe a set of functions that are responsible for forming the DTAP messages and communicating with the LMUs in the network. This fundamental design basis places control of the LMU outside the BTS with no hardware change required on the BTS. Thus, communication between the LMU and SMLC is exclusively over the air interface by DTAP messages with no direct communication.
This distance between the LMU and BTS has a number of disadvantages. Primarily, the Operations and Management (OandM) portion of the network becomes complex since the DTAP message stream must pass several entities within the network. A dedicated channel must be assigned, setup and used to control the LMU designations creating overhead and latency. Since mobiles are often roaming, the added overhead can result in less than the most accurate positioning coordinates for a particular mobile. Additionally, the use of a separate channel ties up network resources which could be better utilized to service customers and increase network capability.
The present invention provides a method and related system of placing a portion of the positioning functions (referred to generally as SMLC) within the BSC portion of the network. Time Of Arrival (TOA) positioning data is delivered to at least one externally operated and maintained requesting agent with a simplified Operations and Maintenance (OandM) for more efficient positioning. Decreased load in the network without tying up unnecessary network resources are some of the advantages.
Disclosed in one embodiment is a system which is capable of delivering Time Of Arrival (TOA) positioning data to at least one externally operated and maintained requesting agent. The system comprises a gateway which provides an interface to the requesting agent. The system also comprises a Base Station Subsystem (BSS), including a Base Transceiver Station (BTS) and a Base Station Controller (BSC). The BSS serves at least one mobile set for which TOA positioning data is requested by the requesting agent via a message transmitted through the gateway.
The BSC can be adapted to maintain a database for relating TDMA number/absolute time for each cell and to receive a positioning via a Master Switching Center (MSC) BSSMAP message. The BSC can be further adapted to determine which LMUs are appropriate for TOA measurement and positioning, where the LMUs are adapted to measure the TOA of HO bursts generated by the mobile and send the result to the BSC.
The BSC can be further adapted to determine and assign channels for positioning handover, as well as to set up a connection to LMUs using the IMSI of the LMUs. The BSC can also be adapted to configure the LMUs for TOA measurement consisting of at least the following configuration data: frequency list, hopping sequence, and absolute time. The BSC can be further adapted to order the mobile to perform positioning handover on the selected channel, pack all measurements from different LMUs and send the composition to the requesting positioning function where final calculation of the mobile positioning coordinates is achieved.
The system further comprises an array of Location Management Units (LMUs) configured to facilitate the computation of positioning coordinates for a mobile set, where the BSS has been equipped with a portion of the Serving Mobile Location Center functions and adapted to determine which of the LMUs are appropriate for making TOA measurements. Specifically, the LMUs are adapted to monitor access bursts and clock the Time Division Multiple Access (TDMA) number with its absolute time. The relation between TDMA frame number and absolute time can then be periodically reported to the BSC by setting up a SDCCH connection where an LMU indicates a new Establishment cause when sending the Channel request. Alternatively, the BSC can request the relationship and time data.
Also disclosed is a method of delivering Time Of Arrival (TOA) positioning data to at least one externally operated and maintained requesting agent. The method comprises the steps of monitoring the synchronization access burst of a mobile and clocking the Time Division Multiple Access (TDMA) number with its absolute time. The relation between the TDMA frame number and the absolute time is then reported to the Base Station Controller (BSC) which could be periodically sent to the BSC or could be reported upon BSC request, according to various embodiments. The relation of TDMA frame number and absolute clock time is reported to the BSC periodically, by setting up a Stand-alone Dedicated Control Channels (SDCCH) connection wherein the LMU indicates a new Establishment cause when sending the Channel request. This relation can be obtained by monitoring the synchronization channel (on the Broadcast Control Channel) (BCCH) or by performing a handover.
The method can also comprise the step of maintaining a database for relation a TDMA number/absolute time for each said cell. This database can be maintained on the BSC. Each cell has a dedicated LMU to report the relation between TDMA frame number and absolute (GPS) time.
The method can further comprise the step of receiving a positioning request via a Mobile Switching Center (MSC) a BSSMAP message. The Positioning Request is received by the BSC and is sent from the MPC to the BSC via the MSC. If the mobile to be positioned is in idle mode, the MSC sets up a call prior to sending the positioning request to the BSC.
The method can further comprise the step of determining which LMUs are appropriate for TOA measurement used in positioning. The LMUs can be adapted to measure the TOA of access bursts generated by the mobile. Based on prevailing radio conditions for the mobile, the appropriate LMUs to be involved are selected by the BSC. The existing locating algorithm (used for cell selection for handover) can be used for this purpose. In addition, a predefined set of neighboring cells (LMUs) can complement the candidate cells (LMUs) selected by locating algorithm.
The method can further comprise the step of determining and assigning channels for positioning handover. The BSC selects a channel for positioning handover with the first choice being the same channel. If the mobile can not handle that, in case of failure due to mobile capability, another channel should be selected. When a positioning emergency occurs, it may be advantageous to select another channel as a first choice. If there is not TCH available, SDCCH should be used.
The method may further comprise the step of setting up a connection to the LMUs by using the IMSI of the LMUs. The BSC sets up a connection for each of the LMUs selected for TOA measurement. This is achieved using the IMSI number of LMUs. For connection, each LMU is paged and set-up is performed.
The method can also comprise the step of ordering the mobile to perform positioning handover on the selected channel. The BSC orders the mobile to perform positioning handover on the selected channel. When the configuration LMU is finished, the process is resumed by sending a Handover Command to the mobile. The Handover Command can specify that handover should be asynchronous as well as the TDMA frame number in which the mobile should start sending access bursts. The BSC predicts this time as the starting time of LMU measurement with the starting time included in the configuration message, and the corresponding FN included in the Handover Command.
A technical advantage of the present invention includes keeping the LMU either outside the BTS or integrated within the BTS to limit the waste of radio resources. By integrating a portion of the positioning or SMLC functionality within the BSC, reduced complexity and improved positioning efficiency is achieved. Since the radio functions in network inherently reside in the BSC, it can be utilized for more efficient positioning.
Another technical advantage of the present invention is reduced complexity of the OandM as the LMU and BSC can communicate directly. The basis for this solution is that the LMUs could be handled by the BSC as a normal network mobile. Furthermore, the BSC is better suited for LMU selection. Thus, by moving a portion of the positioning functions (or SMLC functionality) to the BSC, TOA positioning is quicker.
Other technical advantages include less load in the network, as well as ease in migration of the positioning functions near to or integrated with the BSC.